Quantitative analysis of eumelanin and
pheomelanin in humans, mice, and other animals: a comparative review.
homochromy, crypsis, color change, image analysis, habitat choice,
pheomelanin, eumelanin
As outlined above, melanin itself provides protection against reactive oxygen species and toxic free radicals; but, on the other hand, the process of melanin biosynthesis itself, particularly that of
pheomelanin, has the capacity to generate reactive oxygen species that may cause DNA damage; and intermediates of melanin biosynthesis such as quinones and semiquinones are potentially mutagenic and as such can promote cytogenetic instability.
SOURCE: Q.LI ET AL/SCIENCE 2012 Pigment Eumelanin
Pheomelanin Mixed Mixed Melanosome shape Found in Red- Tufted Double- Microraptor winged titmouse crested blackbird cormorant
Importantly, it is known that the melanogenetic pathway is shifted from eumelanin toward
pheomelanin formation when GSH or cysteine is added to melanocytes or melanoma cell lines.
Pheomelanin coat colour dilution in French cattle breeds is not correlated with the TYR TYRP1 and DCT transcription levels.
In the reaction, tyrosine is first oxidized to dopaquinone, which either cyclises to give a dihydroxyindole precursor of black or brownish eumelanins or reacts with cysteine to give a precursor of reddish brown
pheomelanin [81].
[alpha]-MSH also regulates pigment production and deposition through activation of tyrosinase, the enzyme that catalyzes synthesis of dopaquinone, the first step in melanogenesis [58]; in turn, dopaquinone reacts with intracellular cystine (supplied by the cystine/glutamate transporter, xCT) to produce cysteinyl-dopa, a rate-limiting step in the synthesis of
pheomelanin during inflammation [59].
Melanocytes produce two forms of melanin, black-brown eumelanin and red-yellow
pheomelanin. Skin and hair colour is determined by the total amount and ratio of eumelanin to
pheomelanin.
Another form of melanin is
pheomelanin, a cysteine containing red-brown polymer of benzothiazine units largely responsible for red hair and freckles.
Red hair is caused by a recessive gene on chromosome 16 and has high levels of pigment
pheomelanin. The MC1R variant gene is also linked to freckles.